World energy demand is projected to increase substantially due to an increase in the world's population; improvement of the standard of living in underdeveloped countries; and depletion of the reserves of fossil fuels.
Now, generally recognized by major countries, global climatic changes caused by increasing emissions of greenhouse gases, such as CO2, require that newly developed energy sources must be environmentally compatible and sustainable. Therefore, greener sources of energy are needed to replace or reduce the consumption of fossil fuels. Biomass is a sustainable and renewable source of fuel, with potentially a net zero greenhouse gas impact. Biomass, in particular biomass of plant origin, is recognized as an abundant potential source of fuels and specialty chemicals. See, for example, “Energy production from biomass,” by P. McKendry—Bioresource Technology 83 (2002) pp. 37-46 and “Coordinated development of leading biomass pretreatment technologies” by Wyman et al., Bioresource Technology 96 (2005) pp. 1959-1966. Refined biomass feedstock, such as vegetable oils, starches, and sugars, can be substantially converted to liquid fuels including biodiesel (e.g., methyl or ethyl esters of fatty acids) and ethanol. However, using refined biomass feedstock for fuels and specialty chemicals can divert food sources from animal and human consumption, raising financial and ethical issues.
Inedible biomass can also be used to produce liquid fuels and specialty chemicals. Examples of inedible biomass include agricultural waste (such as bagasse, straw, corn stover, corn husks, and the like) and specifically grown energy crops (like switch grass and saw grass). Other examples include trees, forestry waste, such as wood chips and saw dust from logging operations, or waste from paper and/or paper mills. In addition, aquacultural sources of biomass, such as algae, are also potential feedstocks for producing fuels and chemicals. Inedible biomass generally includes three main components: lignin, amorphous hemi-cellulose, and crystalline cellulose. Certain components (e.g., lignin) can reduce the chemical and physical accessibility of the biomass, which can reduce the susceptibility to chemical and/or enzymatic conversion.
Attempts to produce fuels and specialty chemicals from biomass can suffer low yields of desired products and low value products (e.g., unsaturated, oxygen containing, and/or annular hydrocarbons). Although such low value products can be upgraded into higher value products (e.g., conventional gasoline, jet fuel), upgrading can require specialized and/or costly conversion processes and/or refineries, which are distinct from and incompatible with conventional petroleum-based conversion processes and refineries. Thus, the wide-spread use and implementation of biomass to produce fuels and specialty chemicals at high yields face many challenges.
For example, biomass derived from forestry, agriculture and cellulosic waste materials, due to its compact strong physical construction and its chemical nature containing primarily cellulose, hemicellulose, lignin, mineral matter and other materials, resists conversion processes such as thermal, hydrothermal, and enzymatic processes, which are used to convert said biomass to fuels and chemicals. In particular, the most abundant and useful components for the conversion, the cellulose and hemicellulose, are bundled up and sealed by the protective coating provided by the lignin component. Therefore, a direct exposure of the cellulose and hemicellulose to chemical reagents or even to thermal conditions is prevented by the lignin and other foreign, non-cellulosic substances present. Additionally, any primary product resulting from the contact of the biomass with a chemical reagent or during thermo-decomposition, and derived from one or more of the components in the biomass substance, is diffusionally restricted from escaping the reaction zone due to the lack of bulk accessibility in the biomass particle.
The reaction products and intermediates being restricted in the bulk of the biomass, and remaining in contact within themselves for longer periods, can further interact within themselves, or can interact with unreacted segments of the biomass or with other components present, to form secondary products. These secondary products are not only undesirable, but their presence in the biomass substrate can alter the reaction pathway, thereby causing changes in the yields and kinds of products obtained from the commercial process.
Further, the three major biomass components (cellulose, hemicelluloses and lignin) have different reactivities towards acids and bases, as well as having different thermal stabilities, and decompose at different rates to different products like organic volatiles, chars, water and gases, including CO/CO2. Unfortunately, the production of chars and gases are produced at the expense of the yield of organic volatiles, thus making the known commercial conversion processes inefficient and costly. In particular, in Cellulose Chemistry and Its Application, T. P. Nevell and S. H. Zeronian (Eds), Chapter 11, “Thermal degradation of cellulose”, Ellis Horwood Ltd (1985) p. 266, it was shown that the presence of inorganic compounds, whether indigenous or added, selectively promotes the formation of char at the expense of tarry oils.
Therefore, there is a need for an improved pretreatment process that will modify the biomass-feed in such a way that when subjected to thermo-conversion (e.g., pyrolysis) processes, it will yield more volatile condensable oily products (e.g., organic liquids) and less char, CO/CO2, other gases and water. Furthermore, there is a significant incentive to increase the yield of organic liquid products obtained by pyrolysis and other thermo-conversion processes.